Firefighters at the Sellafield nuclear site are to go on strike for the first time after talks over pay broke down, the GMB union said.

Union members voted to walk out for several 24-hour periods in a dispute over pay grading. It says many firefighters at the plant are performing roles above what they are paid to do, such as paramedic work.

Chris Jukes, GMB senior organiser, said they had attempted to negotiate for several years and had only opted to strike as a "last resort".

A date for the first strike will be set next week. However, union leaders say they were happy to return to the table with Sellafield management for more talks.

Private consortium Nuclear Management Partners is to be stripped of a multibillion-pound contract to clean up the nuclear waste site at Sellafield Credit: PA

Private consortium Nuclear Management Partners is to be stripped of a multibillion-pound contract to clean up the nuclear waste site at Sellafield, the Government has confirmed.

The £9 billion contract will switch to the Nuclear Decommissioning Authority.

Nuclear Management Partners, comprised of US engineering group URS, British firm AMEC and French energy firm AREVA, has run the site for more than six years, and was granted a five-year extension in 2013, despite criticism from unions of its performance.

Energy and Climate Change Secretary Ed Davey said: "Sellafield is the biggest and most complex nuclear site in Europe, so it's right that we keep the way it's being managed under constant review.

"We have seen great examples of how this approach can work with Crossrail and the Olympics - and I'm confident we'll see similar results at Sellafield."

Challenges of cleaning up waste at a Cumbria nuclear site are "unprecedented" and more complex than "any other operational or decommissioning nuclear site in the world", the head of the team overseeing Sellafield nuclear site.

NMP chairman Tom Zarges dodged claims costs were spiralling out of control and said the consortium was focused on building on "our experience of the last five years".

The challenges at Sellafield are unprecedented, with complexities exceeding any other operational or decommissioning nuclear site in the world, therefore demanding extraordinary technology and skills.

The first term of our contract has been characterised by many successes but also a number of disappointments and areas for improvement.

Our job now is to build on our experience of the last five years to safely and reliably deliver our customer's mission, while further accelerating the pace of change and providing value for money to the NDA, Government and the UK taxpayer.

Sellafield Ltd can confirm that the radioactivity detected by one of our in-air monitors overnight is not attributable to any issue or problem with any of our operations on site.

Our in-air monitors are extremely sensitive and pick up on any abnormality. Overnight the monitoring system initially indicated elevated levels of activity. Following investigation and analysis, we can now confirm these levels to be naturally occurring background radon.